Variable air intake ramps for aerospace vehicles
This invention relates to engine air intakes for aerospace vehicles and more particularly to those intake systems comprising a fixed ramp and one or more adjustable ramps by which means air intake flow is matched to propulsion engine demand. 
     Optimised matching of air intake flow to propulsion engine demand is of particular importance if unacceptable performance losses, which may arise from drag due to spillage, shock waves etc, are to be avoided. This is especially the case in aerospace vehicles having wide ranging engine air requirements within the vehicles operating parameters, which may be determined, amongst other things, by Mach number. As is well known in the art, the air intake flow requirements for a high performance engine are such that, at start up, or in the subsonic mode the cross-sectional area of the air intake duct must be large. At transonic speeds, typically M-1.5 the air intake demand will be of a lesser order whereas at speeds approaching M=5 the captured air is more highly compressed, and consequently the intake throat cross-section, will be small. 
     In order to achieve these wide ranging parameters within a single system, it is known to provide two dimensional, variable, air intake ramps for high performance vehicles comprising a plurality of ramps, the most forward of which is fixed, a second ramp hinged at its front edge to the fixed ramp and third and subsequent ramps hinged to each other at their adjacent edges. The number of ramps is determined by the individual air intake configuration, relative movement of the ramp portions varying the air intake geometry. Actuators, for example irreversible screw jacks, interconnect with selected ramps by which means the ramp system is moved synchronously and automatically set by the air intake control system. 
     One of the problems in this arrangement is that the intake flow induces high pressure loads on the ramps and consequently on the ramp actuators. This results in actuators significantly sized to react to these high pressures which may be undesirable or unacceptable in terms of bulk and weight. It is the object of the present invention to provide a variable air intake ramp arrangement including ramp pressure load compensating means, by which means actuator loads a reduced to an acceptable degree. 
     According to the present invention there is provided a variable air intake ramp control arrangement for an aircraft propulsion engine, said air intake control arrangement comprising: 
     an air intake duct, variable geometry ramp means mounted within said air intake duct and movable to selected positions across said air intake duct for controlling the amount of air passing therethrough to match propulsion engine demand and actuator means for moving said ramp means and for reacting induced intake air pressure loads on said ramp means; characterised in that said ramp means, in addition to defining the fluid flow passageway of said air intake duct, further defines the adjacent boundary of an enclosure whose enclosed volume is variable as a function of the adjustment of said ramp means and includes ramp pressure load compensating means whereby for inducing a reacting pressure on said ramp means such that the induced intake air pressure load on said ramp means and said actuator means is correspondingly alleviated. 
    
    
     One embodiment of the invention will now be described, by way of example only, in which: 
     FIG. 1 illustrates, in diagrammatic side elevation port side only drawn, an arrangement of variable air intake system. 
     FIG. 2 is a section through the air intake system viewed along a line II--II in FIG. 1. 
     FIG. 3 depicts a schematic arrangement, in side elevation, of a variable air intake system at a particular operational setting. 
     FIG. 4 depicts the variable air intake system at an alternative setting. 
     FIG. 5 is a part side elevation on the intake viewed in direction of arrow 5 in FIG. 1. 
    
    
     Referring to the drawings, FIG. 1 illustrates a part side elevation on the air intake of the present invention and FIG. 2 is a sectional view through the intake. This indicates that, in this embodiment it is an air intake arrangement mounted upon the side of the aerospace vehicle. Equally, however, it would be applicable to a chin-intake arrangement, ie, an intake mounted to the underside of an aircraft fuselage or wing. 
     As clearly illustrated in FIG. 2 the variable air intake 10 mounted upon a vehicle 11 includes an air intake opening 12 whose opening is defined by a fixed ramp 13 and an intake lip 14. An air intake flow splitter 15 is illustrated but not described further here. The air intake control system includes a variable ramp arrangement comprising a series of interconnected ramp panels, three in number, indicated as 16-18 inclusive on FIGS. 1 and 2. Panel 13 includes a pivotal attachment 19 to the fixed ramp 13 at its forward end and a pivotal attachment 20 at its rearward end to ramp panel 17 which in turn is pivotally attached at 21 to the extreme rearward ramp panel 18 which terminates such that it slidably engages at 22 at guideway 35. Two irreversible screw-jacks 23 and 24 are mounted within the enclosure 25 defined by the ramp elements 16-18 inclusive. The screw jack 23 is pivotally attached at 26 to the vehicle side structure 27 and to the ramp panel 16. A diaphragm 28 extends from the jack ram 29 in a forwardly diagonal direction and is similarly pivotally attached to the vehicle side structure 27. The screw-jack 24 lies substantially in alignment with the guideway 35 and is pivotally interconnected to the ramp panel 18. It is supported at 30 off the vehicle side structure 27. By means of these jack pairs, the geometry of the air intake ramps may be varied in accordance with engine demand parameters to give the desired intake flow. The variable ramp arrangement further includes ram air inlet 31 and outlet 32, communicating with the enclosure 25. 
     Although not illustrated here the forward zone 34, that is the extreme forward portion of the enclosure 25 is permanently vented to the local external airstream. FIGS. 3 and 4 illustrate, by way of example, alternative settings of the intake ramps to meet particular requirements. FIG. 3 illustrates the transonic M=1.5 condition and FIG. 4 the supersonic M=5 condition. 
     The principal object of the present invention is to achieve reasonable jack loads, particularly relevant in this embodiment to the actuator 24 which drives the ramp panel 18 via its engagement in the guideway 35 and by which means, in conjunction with actuation of the forward actuator 23, the ramp geometry is varied automatically in accordance with engine demand. The ramp pressures and consequently the actuator loads are alleviated to a substantial degree by pressurising the enclosure 25 via the ram air inlet 31, which is actively controlled together with the exhaust demanded, the enclosure 25 is vented via the outlet 32 to the local external airstream. The extreme forward zone 34 is permanently vented to the local external airstream.